Interface - The Journal of Wheel/Rail Interaction

FRICTION CONTROL

Drilling Down to Top-of-Rail Friction Control (continued)

The Portland, Ore., Tri-Met system, for example, uses an SRS pump and activation system that is housed beneath a cover plate in the street (see Figure 1 on previous page). A vibration sensor activates the pump and the lubricant is pumped through a 3/16-inch-diameter hole drilled into the rail at a 70-degree angle to the gauge face (see Figure 2). The location of the hole through which the lubricant or friction modifier is applied can be angled more toward the top of rail to provide better top-of-rail coverage, or toward the gauge corner for better gauge-face lubrication. "Provided the output is properly controlled, there's very little waste," Reiff said. This is particularly attractive in public areas with foot traffic.

Also attractive is that the likelihood of over-application of grease or friction modifier is minimized. Significantly less lubricant is applied for every wheel pass when compared to traditional wayside applicators. This also means, however, that each applicator is able to cover a smaller area—one or two curves, at most.

One of the drawbacks to the system is that the applicator can't easily be moved "Once you drill a hole in the rail, it's fixed," Reiff said. There's little in the way of adjustment that can be done. "If the location is not right, if it's too high or too low, a new hole must be drilled." And while transit systems don't change rails as often as freight railroads must, when rail is renewed, a new hole must be drilled.

While most of the Tri-Met applications are in embedded track, an open track site that better accommodated a hand tribometer was used for the tests. Microphones were located outside each track and between them. Four lubricants (three greases and one quasi-friction modifier) were tested over a two-week period. Effectiveness was measured at two carry distances, 200 feet and 1,200 feet from the applicators, which were located near the entrance to 8-degree and 8-degree reverse curves.

Depending on the lubricant, friction levels attained a steady state of about 0.3 at the gauge face and about 0.35 at the top of the rail after 50 - 120 axle passes in the 200-foot zone and 85 - 180 axle passes in the 1,200-foot zone. Effectiveness dropped off significantly beyond 1,500 feet from the applicator.

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